As I was saying, if we were to draw each time we are threatened due to the risks of the unknown, then would it be often...making a bad situation worse.

I see what you're saying.

But think about it...

The road rage guy was driving in an aggressive manner.
He nearly caused the OP to crash.
He jumped out of his car and approached the OP's car.
The OP didn't know whether the road rage guy was armed or not.
The road rage guy actually pounded on the OP's car hood.

At that point the road rage guy could have pulled out a pistol and started shooting.

And at this point the OP's pistol was still under the seat with no round in the chamber.

Think about it...
He is able to pound on the car hood and now he is shooting at you.
How far away do you think he would be shooting from?
Three feet away? Five feet?

The window glass might deflect the first or second round, but after that even the worse shot would probably be able to hit his mark from three to five feet.